Bag set for use in centrifugal separation

ABSTRACT

Apparatus for centrifugal separation of liquid mixtures is disclosed including an inner circular bag and an outer annular bag which has an inner diameter corresponding to the outer diameter of the inner circular bag, a connecting channel for providing fluid communication between the inner and outer bags, and a rigid circular mount for mounting the outer annular bag for centrifugation in a manner such that the outer annular bag adopts a conical configuration by shortening its inner diameter. Methods for centrifugal separation of thrombocyte suspensions and bone marrow cells using this apparatus are also disclosed.

FIELD OF THE INVENTION

The present invention relates to a bag-set intended for batchcentrifugal separation. More particularly, the present invention relatesto a bag-set of the type which comprises an essentially ring-shapedouter bag and an inner bag, formed from the central part of the ring, aswell as one or more connecting channels between the interiors of thesebags.

BACKGROUND OF THE INVENTION

Systems of coupled bags have been used for the centrifugal separation ofblood, blood products and other biological fluids. In these systems, thefluid which is to be separated is supplied to a primary bag of thesystem and after centrifugation and separation of the fluid into two ormore fractions, one or more of these fractions is pressed into theattached or secondary bags. For use in centrifugal separation, speciallyadapted round and ring-shaped or annular bags are known in thisconnection. Bag systems of this type are described e.g. in U.S. Pat.Nos. 4,990,132 and 5,114,396. These documents also disclose how thistype of bag-system can be manufactured from plastic films which aresuperimposed on one another and joined by means of an outer ring-shapedseam and an inner ring-shaped seam, so that a ring-shaped or annularouter bag is formed as well as a plate-shaped or circular inner bag inthe central portion of the ring. It is also possible for severalchambers to be arranged, one upon the other, in the inner bag, dependingon the number of film layers which are sealed together. The inner seamis suitably provided with perforations so that the outer and inner bagscan be separated from each other.

The fluid which is to be separated can thus be supplied to the outerring-shaped bag and after centrifugation is subjected to an externalpressure which presses the fraction which is closest to the center ofthe rotor, through the connecting channel, to the inner bag. Severaldifferent combinations of connected channels can be employed if theinner bag comprises a plurality of chambers. Different methods are alsoknown for achieving the compressive pressure on the bag while it is inthe rotor and undergoing rotation.

From a point of view of cost it is advantageous if the inner bag can bemanufactured from film material which is obtained from the remainingcentral portion of the outer bag. If a large volume is required for theinner bag, this means, however, that the diameter of the outer bag willbe large, which is a disadvantage with many applications and requirescentrifuges with large rotor diameters.

It is therefore an object of the present invention to provide animproved bag-system of the aforementioned type which provides increasedflexibility as regards the choice of the volume of the inner bag and thediameter of the outer bag.

This and other objects and advantages which are described in more detailin the following description, are achieved by a bag-system hereof.

SUMMARY OF THE INVENTION

In accordance with the present invention, these and other objects havenow been accomplished by the invention of centrifugal separationapparatus, primarily for the separation of biological fluids, comprisingan inner circular bag portion having an outer diameter, an outer annularbag portion having an inner diameter corresponding to the outer diameterof the inner circular bag portion, a connecting channel for providingfluid communication between the inner circular bag portion and the outerannular bag portion, and central mounting means comprising a rigidcircular mounting member for mounting the outer annular bag portion forcentrifugation in a manner such that the outer annular bag portionadopts a conical configuration by shortening the inner diameter of theouter annular bag portion.

In a preferred embodiment, the inner circular bag portion and the outerannular bag portion are detachably formed from integral bag formingmaterial. In a preferred embodiment, the apparatus includes a pluralityof connecting channels.

In accordance with another embodiment of the centrifugal separationapparatus of the present invention, the outer annular bag portionincludes an interrupted portion, and further includes a pair of endportions defining the interrupted portion, whereby the outer annular bagportion adopts the conical configuration by wrapping the pair of endportions over each other to thereby shorten the inner diameter of theouter annular bag portion.

In a preferred embodiment, the interrupted portion of the outer annularbag portion has a predetermined length defined by a pair of cuts in theouter annular bag portion to remove a predetermined length of the innerdiameter of the outer annular bag portion.

In accordance with another embodiment of the centrifugal separationapparatus of the present invention, the outer annular bag portionincludes a folded portion whereby the outer annular bag portions adoptsthe conical configuration.

In accordance with another embodiment of the centrifugal separationapparatus of the present invention, the central mounting means includesan inner cavity for mounting the inner circular bag portion, the innercavity being dimensioned so that when the inner circular bag portion ismounted therein, the inner circular bag portion can be filled with afluid by expansion in an axial direction but radial expansion of theinner circular bag portion is restricted.

In accordance with another embodiment of the centrifugal separationapparatus of the present invention, the inner circular bag portionincludes first and second axially disposed compartments, and theconnecting channel comprises a first connecting channel portion forproviding fluid communication with the first axially disposedcompartment and a second connecting channel portion provides fluidcommunication with the second axially disposed compartment.

In a preferred embodiment, the first and second connecting channelportions comprise separate connecting channel members. In anotherembodiment, the first and second channel portions comprises separatebranches of a single connecting channel.

In accordance with another embodiment of the centrifugal separationapparatus of the present invention, the apparatus comprises an innercircular bag portion having an outer diameter, an outer annular bagportion for arrangement concentrically around the inner circular bagportion, the outer annular bag portion having an outer diameter defininga central point, and a connecting channel providing fluid communicationbetween the inner circular bag portion and the outer annular bagportion, the connecting channel being connected to the outer annular bagportion at a connecting point thereon which is displaced inwardly towardthe central point so that the distance between the central point and theconnecting point is less than the outer diameter of the inner circularbag portion.

In a preferred embodiment, the inner circular bag portion and the outerannular bag portion are detachably formed from integral bag formingmaterial. Preferably, a plurality of connecting channels are provided.

In accordance with another embodiment of the centrifugal separationapparatus of the present invention, the outer annular bag portionincludes a radially inwardly projecting portion, and the connectingpoint is located in the radially inwardly projecting portion.

In accordance with another embodiment of the centrifugal separationapparatus of the present invention, the outer annular bag portion iseccentrically disposed with respect to the inner circular bag portion,whereby the outer annular bag portion includes a first width on a firstside thereof and a second width on a second opposite side thereof, thefirst width being greater than the second width, and the connectingpoint being located at the first width.

In a preferred embodiment, the connecting point is located adjacent tothe inner diameter of the outer annular bag portion.

In accordance with the present invention, a method is also provided forcentrifugal separation of thrombocyte suspensions from buffycoatfractions utilizing an inner circular bag portion having an outerdiameter and an outer annular bag portion having an inner diametercorresponding to the outer diameter of the inner circular bag portion,the method including connecting the inner and outer bag portions forfluid communication therebetween, mounting the annular bag portion forcentrifugation in a manner such that the outer annular bag portionadopts a conical configuration by shortening the inner diameter of theouter annular bag portion, and conducting the centrifugation forobtaining thrombocyte suspensions and separating the thrombocytesuspensions from the outer annular bag portion to the inner circular bagportion.

In accordance with the present invention, methods are also provided forcentrifugal separation of bone marrow cells from bone marrow suspensionsutilizing an inner circular bag portion having an outer diameter and anouter annular bag portion arranged concentrically around the innercircular bag portion, the outer annular bag portion having an outerdiameter defining a central point, the method comprising connecting theinner circular bag portion to the outer annular bag portion for fluidcommunication therebetween at the outer annular bag portion at aconnecting point therein which is displaced inwardly towards the centralpoint so that the distance between the central point and the connectingpoint is less than the outer diameter of the inner circular bag portion,thereby separating the bone marrow cells from the bone marrowsuspension, and separating the bone marrow cells into the inner circularbag portion therefrom. In a preferred embodiment, this method includesseparating the bone marrow suspensions into three fractions including aintermediate buffycoat suspension, separating the intermediate buffycoatfraction into three separate fractions including a bone marrowcontaining intermediate fraction, and washing the bone marrow containingintermediate fraction.

In accordance with the present invention, the bag-set comprises anessentially ring-shaped outer bag and an inner bag, formed from thecentral part of the ring and preferably being detachable from the ring,as well as one or more connecting channels between the interiors ofthese bags. According to the present invention the bag-system furthercomprises a rigid, circular mounting member on which the outer bag ismounted in a position for centrifugation whereby the outer bag is givena conical shape around the mounting member by means of a contractivering-shortening.

The mounting member also performs the function of facilitating thehandling of the bag-set, as well as fixing the inner bag in its intendedposition for centrifugation. The mounting member has an inner cavity, inwhich the inner bag is placed in a manner which limits its radialexpansion but which permits expansion in the axial direction when it isfilled with fluid. The inner cavity has a diameter which is less thanthe diameter of the inner bag, whereby the inner bag is pressed into thecavity so that its peripheral part curves along the walls of the cavity.The center part preferable has essentially the form of a downwardly-opencylinder.

The contractive ring-shortening of the outer bag can be achieved by asection of the ring being gathered together into a fold. The innerring-shaped fluid communication in the bag is thereby blocked. The foldcan be placed on the ring so that two overlapping bag ends are obtained,as well as a material piece between the bag ends which remains empty andblocked for fluid flow. The outer bag can also be cut and the resultingfree ends sealed. The shortening of the bag can then be achieved bydrawing the ends together so that they overlap each other. The bag canalso be cut in two places and the intermediate material piece removed,whereby the free ends are drawn towards each other in a correspondingmanner until they overlap.

Due to the fact that the circular-shaped fluid communication in theouter bag is blocked or interrupted, a flow of the fluid around the bagwhen the centrifuge accelerates or retards is prevented, whichaccelerates commencement of the separation procedure and preventssilting up when the rotor is slowed down.

The separation chamber in the rotor is adapted to the conical form ofthe shortened outer bag. In view of the fact that separation occurs in aradial direction in a relatively narrow conical chamber, an angularseparation effect, as well as a fast separation, are achieved. Theseparation path in the radial direction is short and the specificheavier component of the fluid travels only a short distance before itmeets an oblique surface which leads it to the bottom part of theconical chamber.

Central placement of the inner bag in the middle of the rotor, combinedwith a limited expansion in the radial direction, means that the fluidwhich is taken up in the inner bag is subjected to a limited field offorce. This has shown itself to be particularly important whenrecovering particle suspensions, e.g. thrombocyte suspensions, since are-sedimentation and undesirable aggregate formation of the particlesmust be avoided.

The bag-set according to the present invention is also particularlysuitable for the recovery of bone marrow cells by centrifugal separationof bone marrow suspensions.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described in more detail withreference to the accompanying figures, in which:

FIG. 1 is a top, elevational view of an embodiment of an outer and aninner bag for a bag-set according to the present invention;

FIG. 2 is a top, elevational view of another embodiment of an outer andinner bag according to the present invention;

FIG. 3 is a side, elevational, partially cross-sectional view of a rigidmounting member for use with a bag-set according to the presentinvention;

FIG. 4 is a top, elevational, sectional view of the mounting memberaccording in FIG. 3;

FIG. 5 is a side, elevational, sectional view of a bag-set according tothe present invention utilizing a rigid mounting member according toFIGS. 3-4;

FIG. 6 is a top, elevational, partially cross-sectional view of thebag-set according to FIG. 5;

FIG. 7 is a side, elevational, sectional view of a bag-set according tothe present invention with double inner bag chambers, mounted in acentrifuge rotor;

FIG. 8 is a top, elevational view of the centrifuge rotor for use inaccordance with the present invention;

FIG. 9 is a side, elevational, schematic view showing use of a bag-setaccording to the present invention during recovery of thrombocytesuspension;

FIG. 10 is a side, elevational, schematic view showing a further stageof use of a bag set according to the present invention during recoveryof thrombocyte suspension; and

FIG. 11 is a side, elevational, schematic view showing a further stageof use of a bag set according to the present invention during recoveryof thrombocyte suspension.

DETAILED DESCRIPTION

Referring to the Figures, in which like reference numerals refer to likeelements thereof, FIG. 1 shows an embodiment of an essentiallyring-shaped outer bag 1 and a central, essentially circular, inner bag 2formed from the central portion of the ring. The interiors of the bagsare joined with a tube 3 having an orifice 4 in the outer bag and anorifice 5 in the inner bag. The outer bag is provided with an additionalconnection 6 for supplying and removing fluid to and from the outer bag.The orifice 4 is placed in a radially inwardly directed bulge 7 of theouter bag. When the lighter enriched phase against the center of therotor is pressed out of the outer bag after separation by means ofpressure being applied thereto, vortex formation can easily occur aroundthe outlet opening, and parts of the next phase can be sucked out. Byplacing the orifice 4 on a bulge which extends radially further inwardlythan the other parts of the outer bag, and by forming the rotor so thatthis part of the bag forms a relatively narrow gap between the rotor andthe rotor cover in the vertical direction, vortex formation around theorifice 4 can be avoided and the lighter phase can be recovered withboth a high quality and high yield.

The outer bag is further provided with a number of attachment means,e.g. eyelets 8, for attachment of the outer bag onto a stiff centerpart, which will be described in more detail with reference to FIGS.4-7.

The bags are produced by two plastic films being placed over each otherand sealed together with an outer ring weld 9 and an inner ring weld 10.The latter weld is such that it either separates the bags totally fromeach other or makes them separable from each other by tearing off.

FIG. 2 shows a somewhat different embodiment of a bag according to thepresent invention, and differs from the embodiment which has beendescribed with reference to FIG. 1 in that the inner ring weld 10 issomewhat eccentrically placed with respect to the outer circumference.The outer bag is thereby wider in the area of the orifice 4 of tube 3 inthe outer bag. This wider portion fulfills the same function as thebulge 7 in the embodiment according to FIG. 1. The wider part of theouter bag is placed in a corresponding manner in the narrow gap betweenthe rotor and the rotor cover. Details which correspond to each other inthe figures have been denoted with the same reference numeral. Thering-shape of the outer bag is cut, and the resulting free ends 11 and12 are closed. The cutting can e.g. be carried out by means of a weld,which at the same time seals the ends. In the embodiment shown in FIG. 2the outer bag is cut with two substantially radially directed welds 13and 14 at a certain distance from each other. The intermediate materialpiece 15 is removed. The essentially ring-shaped outer bag is thus freefrom any circulating inner fluid communication.

In order to reduce the diameter which is taken up by the bag-system andat the same time facilitate handling of the bags and fixing of same intheir intended positions for centrifugation, a rigid circular mountingmember 16 is used. The outer bag is mounted around the outside of themounting member and the inner bag inside in an inner cavity 17 in themounting member.

The bag-set can thereby be lifted into and out of the rotor with asimple hand grip. FIGS. 3 and 4 show an embodiment of such a mountingmember in the form of a downwardly-open cylinder. FIG. 3 shows asectional view through the mounting member, and FIG. 4 shows themounting member in horizontal section. The cylinder, at its open end, isprovided with a conical inclined rim 18, in which the outer bag's inneredge is fastened in the fastening means 19 which cooperate with thefastening eyelets 8 in the outer bag. On its inside the cylinder hasholders 20 and 21 for fixing the connection tube 3 between the outer andthe inner bag, and is provided with openings 22 and 23 for access to thetube from the upper side of the mounting member, to allow attachment ofclamp valves or optical sensors etc. onto the tube when the bag-systemis placed in the rotor.

FIGS. 5 and 6 show a complete bag-system with the mounting member insection, and in horizontal view, respectively. The inner bag 2 is placedinside the mounting member 16, which is arranged to limit the radialspreading of the inner bag but to allow for axial expansion of the innerbag when this is filled with a fluid. In the figures a mounting memberis shown in the form of a cylinder according to FIGS. 3-4. The cylinderhas a smaller diameter than the bag which is pressed into the cylinderso that its peripheral part 25 is folded and rests against the innersurface of the cylinder. When the inner bag is filled it expands in thevertical direction inside the cylinder. The folding of the inner bag'speripheral part, which is the result of its having a larger diameterthan the mounting member 16, has shown itself to have only a marginalimpact upon the maximum volume which can be taken up in the inner bag.

The outer bag 1 has too large a diameter for its inner edge to fit ontothe rim 18. In connection with mounting onto the center part, thering-shaped outer bag is shortened by a section of the ring being drawntogether into a fold 24 which is laid onto the ring. The continuousfluid communication in the ring is thereby broken. In the case where thering is cut by a weld or the like, the ring is shortened by the endbeing laid in overlapping relationship. With shortening of the ring, thebag will assume a conical shape without being folded, and can easily befastened to the conically inclined rim 18 formed in the same way on thecylinder 16. In this way the bag-system has a small diameter and can beused in small centrifuge rotors despite the bags being manufactured witha diameter which is dependent on the volume which the inner bag 2 isdesired to have, i.e. the central section of the outer bag.

FIG. 7 shows a section through a bag-system placed in a centrifuge rotor26 adapted to the system hereof. In this case the bag-set has an innerbag with an upper chamber 27 and a lower chamber 28. FIG. 8 shows therotor as seen from above. Reference numeral 29 denotes the base of therotor, and reference numeral 30 its cover. A channel 31 for hydraulicfluid passes through the axis of the rotor to the rotor's ring chamber32 where a ring-shaped hydraulic chamber 33 is delimited from the restof the ring chamber by a membrane 34. The outer bag is placed in thering chamber, and its bulging portion 7 is positioned in the gap 35between the base of the rotor and its cover. The connection tube 3 whichhas an orifice in the bulge 7 in the outer bag, branches into a branch36 which has an orifice in the upper inner bag chamber 27 and a branch37 which has an orifice in the lower chamber 28. The branch conduits areplaced in clamp valves 38 and 39 which are controlled by the programmedoperation of the centrifuge and/or photocells which detect displacementof the boundary surface of the phase in the connection tube 3. The outerbag is connected with an additional tube 6 which is drawn up through thehole 22 in the mounting member and further through a hole 40 in therotor cover. The tube is used for filling the outer container with thefluid which is to be separated, and is thus accessible from the outsideof the rotor. After filling of the outer container the tube is closedwith tube welding tongs and is placed in a groove 41 in the rotor cover.

Instead of a branched connector tube 3, the outer bag can be connectedto each of the chambers in the inner bag by means of separate tubes andone-way valves.

The bag-set according to the present invention can thus be used for theseparation of blood and other biological fluids and with treatment ofsuch fluids with different components. The system with double inner bagchambers and a branched connector tube between outer and inner bags canbe used when a separation into three different fractions should occur.Two fractions are each led to their respective inner bag chamber, andthe third fraction remains in the outer bag.

The bag-set according to the present invention is specially adapted forrecovering thrombocyte suspensions from isolated buffycoat fractions,which is schematically shown in FIGS. 9-11. Buffycoat is recovered as anintermediate fraction by centrifugal separation of whole blood. A numberof buffycoats 42, e.g. six, are transferred through tube 6 to the outerbag 1, upon which the tube 6 is cut and sealed with tube welding tongs(FIG. 9). The buffycoats are centrifuged and divided up in athrombocyte-rich plasma 43 and a remaining volume 44 (FIG. 10). Thiscentrifugation occurs with a certain amount of care in order to avoidcentrifuging out of the thrombocyte cells. The conical angulation of theouter bag and the relatively small diameter are thereby a largeadvantage. Pressure is thereafter brought to bear on the outer bag, andthe thrombocyte suspension is pressed during on-going centrifugation viathe tube 3 to the inner bag 2 (FIG. 11). The inner bag will therebyexpand in the vertical direction, while its radial expansion is fixed bythe mounting member (not shown).

Since the thrombocyte suspension is transferred to the center of therotor and is maintained in a limited area in the radial direction, itwill only be subjected to a weak centrifugal force as soon as it isrecovered. If the thrombocyte suspension is subjected to a lengthystrong centrifugal force, an undesired aggregate formation occurs, alongwith a loss of thrombocyte cells. The special requirements which aremade for recovery of thrombocyte suspension of high quality and highyield are thus fulfilled by the bag-set according to the presentinvention.

Another field of application in which the bag-set according to thepresent invention is especially suitable is bone marrow separation. Bonemarrow separation is applied in connection with cancer treatments usinglarge doses of radiation treatment. Bone marrow is taken out of thepatient before the radiation treatment and, through various separationsand washing procedures, bone marrow cells are isolated which arere-transfused after the radiation treatment.

A known procedure for isolation of bone marrow cells comprises thefollowing steps:

a) centrifugal separation of bone marrow suspension in three fractionsand collecting the intermediate fraction, or buffycoat;

b) the buffycoat fraction from step (a) is centrifuged one more time ina separation fluid, commonly Ficoll (a trademark of Pharmacia FineChemicals AB), and an intermediate fraction which contains the bonemarrow cells is collected; and

c) washing of the collected fraction from step (b) for recovery ofre-transfusable bone marrow cells.

The bag-set according to the present invention can be used in such aprocess in the following manner:

In step (a) a bag-set with double chambers in the inner bag is used,including a branched connection conduit from the outer bag to the innerbags, i.e. of the type which is shown in FIG. 7. The outer bag issupplied with a batch of bone marrow suspension, which by means ofcentrifugation is divided up into plasma, buffycoat (comprising the bonemarrow cells) and remaining products. Due to the influence of pressureon the outer bag the plasma fraction is thereafter pressed, duringon-going rotation, to the first inner bag, and thereafter a determinedamount of buffycoat is pressed to the second inner bag, the remainingproducts being left in the outer bag.

In step (b) a similar bag-system as in step (a) is used. The separationfluid (Ficoll) is supplied to the outer bag and a suspension of thebuffycoat fraction from step (a) is added carefully so that it forms alayer above the separation fluid. The centrifuge is started slowly sothat mixing is avoided. Depending on the specific weight of the cells,they will migrate through the separation fluid or stay above same duringcentrifugation. The bone marrow cells are enriched in a layer above theseparation fluid. The supernate (plasma) is thereafter pressed, duringon-going centrifugation, into the first inner bag chamber, andthereafter an intermediate fraction consisting of the layer closestabove the separation fluid (containing the bone marrow cells) is pressedinto the second inner bag chamber. The heavier cell material remains inthe outer bag.

In step (c) a bag-system with a single chamber inner bag can be used,i.e., of the type which is described with reference to FIG. 5. Thefraction of bone marrow cells contaminated with separation fluid fromstep (b) is transferred to the outer bag, and a suitable washing fluidis supplied. After centrifugation the used washing fluid is pressed outinto the inner bag. New washing fluid can then be supplied to the outerbag via a tube (such as that shown in FIG. 7), which is accessible fromthe outside of the rotor cover, and the washing procedure can berepeated as required. The washed bone marrow cells are isolated in theouter bag.

With the bag-set according to the present invention a cheaply pricedtreatment set can be obtained, which allows for the separation ofbiological fluids during on-going centrifugation into separate componentcontainers without the fluids passing complicated, expensive andsterility-unsafe rotating couplings. Despite a small diameter, which canbe adopted to an existing centrifuge type, relative large volumes can betaken up in the inner bag. The bag-system is therefore useable for manydifferent types of separations.

Although the invention herein has been described with reference toparticular embodiments, it is to be understood that these embodimentsare merely illustrative of the principles and applications of thepresent invention. It is therefore to be understood that numerousmodifications may be made to the illustrative embodiments and that otherarrangements may be devised without departing from the spirit and scopeof the present invention as defined by the appended claims.

We claim:
 1. Apparatus for use in a centrifugal separator, saidapparatus comprising an inner circular bag portion having an outerdiameter, an outer annular bag portion having an inner diametercorresponding to said outer diameter of said inner circular bag portion,and a connecting channel for providing fluid communication between saidinner circular bag portion and said outer annular bag portion, saidouter annular bag portion being separable from said inner circular bagportion and including an interrupted portion, and including a pair ofend portions defining said interrupted portion, whereby said outerannular bag portion adopts said conical configuration by wrapping saidpair of end portions over each other to thereby shorten said innerdiameter of said outer annular bag portion.
 2. The apparatus of claim 1wherein said end portions of said outer annular bag portion are definedby a pair of cuts in said outer annular bag portion removing apredetermined length of said outer annular bag portion.
 3. Apparatus foruse in a centrifugal separator, said apparatus comprising an innercircular bag portion having an outer diameter, an outer annular bagportion for arrangement around said inner circular bag portion, and aconnecting channel providing fluid communication between said innercircular bag portion and said outer circular bag portion, saidconnecting channel being connected to said outer annular bag portion ata connecting point thereon, said outer annular bag portion beingeccentrically disposed with respect to said inner circular bag portion,whereby said outer annular bag portion includes a first width on a firstside thereof and a second width on a second side thereof, said firstwidth being greater than said second width, and wherein said connectingpoint is located at said first width.
 4. The apparatus of claim 3wherein said connecting point is located adjacent to the inner diameterof said outer annular bag portion.
 5. A bag set for use in theseparation of fluids by centrifugation in a centrifuge of a type havinga rotor with a processing space concentric to the axis of rotation ofsaid rotor, said processing space comprising a central rotor compartmentand a conical, annular rotor compartment, and having means for reducingthe volume of said annular rotor compartment during rotation of saidrotor, said bag set being intended for insertion into said processingspace and comprising a rigid circular mounting member adapted to fitinto said central rotor compartment, said mounting member including aninner cavity extending in the direction of said axis of rotation of saidrotor, an outer essentially ring-shaped bag of flexible material mountedaround said mounting member in a conical configuration and adapted tofit into said annular rotor compartment and be supplied with said fluidwhich is to be separated, an inner circular bag of flexible materialseparable from said outer ring-shaped bag and mounted in said innercavity and adapted to receive a fluid from said outer bag when thevolume of said annular rotor compartment is reduced, said inner cavitybeing arranged to limit the spreading of said inner bag in the radialdirection of said rotor but to allow expansion of said inner bag in thedirection of said axis of rotation of said rotor when said inner bag isfilled with a fluid, and a connecting tube for providing fluidcommunication between said outer conically configured ring-shaped bagand said inner bag in said inner cavity.
 6. The bag set of claim 5wherein said inner circular bag and said outer ring-shaped bag aredetachably formed from superposed sheets of plastic film material,whereby said inner circular bag is formed from a central portionsurrounded by said outer ring-shaped bag.
 7. The bag set of claim 6wherein said outer ring-shaped bag is eccentrically disposed withrespect to said inner circular bag, whereby said outer bag includes afirst width on a first side thereof and a second width on a second sidethereof, said first width being greater than said second width, andwherein said connecting tube is connected to said outer bag at saidfirst width.
 8. The bag set of claim 5 wherein said outer ring-shapedbag comprises a ring section having a fold directed substantiallyradially across said ring section, said folded section being laid ontosaid ring as an overlap when said outer ring-shaped bag is mountedaround said mounting member in said conical configuration.
 9. The bagset of claim 5 wherein said outer ring-shaped bag comprises a pair ofopposed, sealed end portions, said pair of end portions overlapping eachother when said ring-shaped bag is mounted around said mounting memberin said conical configuration.
 10. The bag set of claim 5 wherein saidconnecting tube is connected to said outer ring-shaped bag at an area ofsaid bag which is situated closest to the axis of rotation of said rotorwhen said bag set is positioned in said processing space.
 11. The bagset of claim 10 wherein said outer ring-shaped bag comprises a radiallyinwardly projecting portion, and wherein said connecting tube isconnected to said outer ring-shaped bag in said radially inwardlyprojecting portion.
 12. The bag set of claim 5 wherein said circularinner bag comprises at least two bag chambers comprising first andsecond bag chambers.
 13. The bag set of claim 12 including a pluralityof connecting tubes for providing fluid communication between said outerbag and each of said first and second bag chambers.
 14. The bag set ofclaim 5 wherein said connecting tube is branched and comprises at leastfirst and second tube branches connected to said first and second bagchambers.
 15. A method for centrifugal separation of bone marrow cellsfrom bone marrow suspensions utilizing the bag set of claim 14 and acentrifuge of a type having a rotor with a processing space concentricto the axis of rotation of said rotor, which processing space comprisesa central rotor compartment and a conical annular rotor compartment, andhaving means for reducing the volume of said annular rotor compartmentduring rotation of said rotor, said method comprising supplying saidbone marrow suspension to said outer ring-shaped bag, centrifuging saidbone marrow suspension to separate said bone marrow suspension to alight plasma fraction, an intermediate buffycoat fraction, and a denserfraction of remaining products, expelling said light plasma fractionfrom said outer bag to said first bag chamber through said branchedconnecting tube and thereafter expelling said intermediate buffycoatfraction to said second bag chamber through said branched connectingtube during rotation of said rotor by reducing the volume of saidannular rotor compartment, and collecting said intermediate buffycoatfraction from said second bag chamber for continued separation.
 16. Themethod of claim 15, wherein said bag set comprises a first bag set andincluding providing a second bag set, supplying a separation fluid tosaid outer ring-shaped bag of said second bag set, supplying saidintermediate buffycoat fraction collected in said first bag set as alayer above said separation fluid in said outer bag of said second bagset, centrifuging said collected fraction with said separation fluid insaid outer bag of said second bag set to separate said collectedfraction into a light plasma fraction, an intermediate fraction disposedin a layer above said separation fluid and a denser fraction, expellingsaid light plasma fraction from said outer bag of said second bag set tosaid first bag chamber of said second bag set through said branchedconnecting tube, and thereafter expelling said intermediate fraction tosaid second bag chamber of said second bag set through said branchedconnecting tube during rotation of said rotor by reducing the volume ofsaid annular rotor compartment, collecting said intermediate fractioncontaining said bone marrow cells from said second bag chamber of saidsecond bag set for continued treatment, and washing said collectedintermediate fraction to obtain re-transfusible bone marrow cells.
 17. Amethod for centrifugal separation of thrombocyte suspensions frombuffycoat obtained from separations of whole blood utilizing the bag setof claim 5 and a centrifuge of a type having a rotor with a processingspace concentric to the axis of rotation of said rotor, said processingspace comprising a central rotor compartment and a conical annular rotorcompartment and having means for reducing the volume of said annularrotor compartment during rotation of said rotor, said method comprisingsupplying said buffycoat to said outer ring-shaped bag, centrifugingsaid buffycoat to separate said buffycoat into a light phase comprisingsaid thrombocyte suspension and a denser phase of remaining products,expelling said thrombocyte suspension from said outer bag to said innerbag through said connecting tube during rotation of said rotor byreducing the volume of said annular rotor compartment, and obtainingsaid thrombocyte suspension in said inner bag.
 18. Apparatus for use ina centrifugal separator comprising an inner circular bag portion havingan outer diameter, and an outer annular bag portion having an innerdiameter corresponding to said outer diameter of said inner circular bagportion, and a connecting channel for providing fluid communicationbetween said inner circular bag portion and said outer annular bagportion, said outer annular bag portion including an interrupted portionand a pair of end portions defining said interrupted portions, said endportions being defined by a pair of cuts in said outer annular bagportion removing a predetermined length of the said outer annular bagportion, whereby said outer annular bag portion can adopt a conicalconfiguration by wrapping said pair of end portions over each other tothereby shorten said inner diameter of said outer annular bag portion.